芦生演習林のスギ伏条稚樹

Abstract

1977年5月および6月, 芦生演習林17林班において, スギ伏条稚樹の調査, とくに上層木の伐採後に生長が期待できそうかどうかについて調査をおこなった。1976年調査の5コのプロットから, 10×10mのサププロットを1コづつ選び, 下層植生の全部について, 地際直径(D_o), 樹幹長 (L) および樹種を測定し記録した。また1つのサブプロットの半分の面積から掘取った, 47個体について, 葉, 枝, 幹, 地中幹, 根などの重量を測定した。下層植生は, 上層林冠の疎開したところで樹種も多く, 相対的な被度も高く, 平均個体も大きくなり, 上層林冠の閉鎖したところよりよく発達する。スギ伏条稚樹は立木本数で, 2, 700本/ha程度と見積もられた。スギ伏条稚樹の各部重量測定結果から, 直径階ごとに, 全個体に占める各部の比を計算すると, 根, 幹の重量比はあまり変化しないが, 枝は著しく増加, 地中幹と葉は漸減の傾向を示す。40cm径級の上層木伐採をおこなうと, 蓄積の50％, 233m_3/ha, 本数で20％, 136本/haが収穫されることになり, 更新面には550本/haが残されることになる。下層植生のうち極端な小径木や大径木は, 伐採による環境の変化に耐えられないであろうから, 生き残るのは, 1000本/ha程度となるであろう。したがって高木, 亜高木, 低木層をあわせて1, 550本/haが更新面に残されるということになる。

The undergrowths with reference to regenerative potentiality of Cryptomeria layerings of the natural stand of Cryptomeria were investigated in May and June, 1977, at Ashiu school forest, Kyoto. The diameter at ground (D0), stem length (L) and the tree species of all the undergrowths occurred were measured and recorded in 5 subplots of 10×10 m established in the 17th compartment. The leaves (wl), branches (wb), stems (ws), underground stems (wau) nd roots (wr) of 47 samples digged out from the half the area of a subplot were weighed. The undergrowths under open canopy were abundant in specific composition, greater in coverage and size of an individual than those under close canopy. The Cryptomeria layerings averaged to 2, 700 trees/ha. Weight ratio of stems and roots to whole individuals were calculated to remain constant with the increase of diameter, while that of branches increase remarkably, and that of leaves and underground stems decrease. According to the recommended working plan to be adopted in the forest stand concerned, the trees of larger diameter class than 40 cm are to be felled, by which 50% by volume or 233 m3/ha, 20% by stocks or 136 trees/ha are to be harvested, and 110 m3/ha, 550 trees/ha are to be reserved. By the effect of break of canopy, violent shift of the water economy and light intensity incident to the forest floor, the growing situation of the undergrowths should be affected impatiently at least to those too small or too large layerings. About 1, 000 out of 2, 700 layerings are estimated to survive and deserve the treatment for regeneration.